Information files are generally stored in magnetic media, disks or tapes. None of these media can achieve a total guarantee of availability. The unavailability of a medium may have multiple causes, ranging from simple error, which can be repaired to restore the entire file contained in the medium, to the complete destruction of the physical medium and its files. Even though non-rewritable digital optical disks, for instance, guarantee file fidelity and durability, the physical medium can still become damaged, for instance when being handled. A method of file management is accordingly necessary, in order not to lose the data in the files.
At present, file management and file archiving consists of making one or more copies on similar recording media in order to increase their availability. However, files evolve, beginning with their development, and frequently go through several versions. This evolution presents a grave problem in the event that the machine that handles the files breaks down, or in the event of partial or total deterioration of the medium on which the files are stored.
A disk defect can be repaired, and the disk may become entirely or partially available again. Similarly, a machine breakdown can erase a new part of the file, and its repair can leave the user in either a certain situation or an uncertain configuration. The problem becomes much more serious when the files can be handled by various persons through various remotely located machines. For these persons, it becomes imperative to manage the availability of files and of their various versions without the risk of losing their updated version or creating an inconsistency in the existence of various available versions.
However, the current solution for file management presents one major problem in the event of intermittent breakdown in at least one of their media. The classic solution is to increment the numbers of successive versions by one unit. Thus if one of the media fails in a breakdown, one can find out which of the available versions is the most recent simply by looking at the numbers of the available versions on the other media. However, when working fast, this solution proves inadequate because of intermittent failures in at least one of the media. For example, let it be assumed that there are five identical copies of version 1 on five respective media. A user makes a modification in one of the media, producing version 2. If the medium becomes unavailable, the user or other users of the same machine or other machines then looks among the four identical versions carrying the number 1 to update them and make a new version, which will then be called version 2. Eventually, the disk that failed will have been repaired, and the repaired disk is returned to service, making the first version available; this version also carries number 2, but it is normally different from the second version number 2 made on the other media. Confusion ensues, producing varying files having the same version numbers. Moreover, another intermittent failure in one of the media will produce renewed confusion. It will be appreciated that in practice, the copies rapidly become inconsistent.